\section{TEST METHODOLOGY}

The main objective was to obtain the engine dynamics, relating the deflection in the throttle lever to the shaft's rotation speed. In the tests conducted, the change in the rotation has been related to the change in the servo PWM signal. However, the servo motor has a particular dynamics, relating a change in the input pulse width to an output angle, which greatly influences the results.  So, if the servo dynamics is well known, its influence can be subtracted from the results. This methodology is sketched in figure \ref{fig:db_dinam}.

\begin{figure}[h!]
\centering
\includegraphics[angle=0, width=0.6\textwidth]{Figura_1.pdf}
\caption{System's dynamics block diagram.}
\label{fig:db_dinam}
\end{figure}

A test was conducted to obtain the model for the particular servo used in this work. The LabView VI developed for this work was used to generate a square wave signal to the a micro-controller unit (MCU). For details, please refer to section \ref{sec:inst}~ Then, the MCU generated an adequate PWM signal from this commanded input and sent it to the servo, concurrently reading its position from an internal potentiometer with one of its 10bit-ADC channels. Finally the MCU sent the signals back to the LabView VI using the computer's serial port. The servo commanded and actual positions were recorded along time. From these results, a complete servo model was identified (section \ref{sec:identification}~ ). This model was introduced in the Box 1 in figure \ref{fig:db_dinam} and, assuming a transfer function model for the Box 2, the results obtained for the whole system (servo + engine) were used to perform the parameter identification for Box 2.
In this way, the resultant dynamics is representative of the engine alone and could be used in conjunction with any other servo, as long as the new servo dynamics is known. 
